This invention relates to footwear, and particularly to athletic footwear.
In copending application Ser. No. 510,671, is disclosed footwear incorporating a special propulsion plate extending from the medial portion of the heel through the arch to a position forwardly of the metatarsal heads. This construction has been found highly effective in cooperating with the spring energy of the natural biomechanism of the foot, storing energy and then releasing the energy in response to flexure during each step. This specially configurated plate is formed of layers of oriented fibers, normally carbon (graphite) fiber, embedded in polymer. Each plate is specially formed and configurated to fit the left foot, or formed to fit the right foot, and is formed of the size necessary. The cost of making each unit and the required inventory of units for a variety of shoe sizes is substantial, as can be readily realized.
The midsole for athletic shoes is typically formed of a foam polymer such as expanded ethylene vinyl acetate polymer (EVA). Such midsole materials break down with usage, thereby lessening control by a runner of his/her feet, and also shortening shoe life.